please help me

Hi,
I am a beginner writing a boot loader. I use gas to write it and got a
weird issue. The following code just try to show out the screen the
symbol "1" ten times

.code16
.section .text
.globl _start
_start:
        movw    $STACK_SEGMENT, %sp
        movw    %sp, %ss
        movw    $STACK_SIZE, %sp
        pushw   %cs
        popw    %ds
        pushw   $SCREEN_SEGMENT
        popw    %es
        jmp     show_banner
 
show_banner:
        movb    $0x07, %ah #white on black
        movb    char, %al  #show this char
        movw    $10,  %cx  #show this char 10 times
        movw    $0, %di    #show at 0,0
run_banner:
        movw    %ax, %es:(%di)
        inc     %di
        inc     %di
        loop    run_banner
 
die:    jmp     die
 
#.section .data
char:   .ascii "1"
.org 510
boot_flag:      .word 0xAA55
                                                                                                                             
#constants
.equ STACK_SEGMENT     , 0x9000      # Top of conventional memory
.equ STACK_SIZE        , 0xffff      # 64K - 1 bytes of stack
.equ SCREEN_SEGMENT    , 0xb800



However, when running, it shows out a symbol in the extend ascii table
instead of "1" !!!?
It seems I cannot reference to the "char" memory location. Why?

How can I debug the binary?

Any help is appreciated.

Tuha.